There are increasing numbers of survivors of trauma in the general population, therefore, it is crucial to understand who does and does not develop PTSD when faced with a trauma. The proposed F31 research takes advantage of an unprecedented ability to examine PTSD before and after one of the largest earthquakes in history that occurred in 2010 off of the central coast of Chile. As the Chilean disaster occurred i the midst of an existing longitudinal prospective cohort study, the proposed study provides a rare opportunity to study adults located at the epicenter of the disaster (N=2,839) who had undergone a structured diagnostic psychiatric interview prior to exposure to a major traumatic event. Pre-disaster Axis I psychiatric disorders (including a PTSD diagnosis) were assessed using the Composite International Diagnostic Interview (CIDI; a comprehensive fully structured diagnostic assessment). One year after the disaster, a modified version of the PTSD module of the CIDI, tailored to measure PTSD from the disaster only, was administered. This presents the ability to uniquely examine the longitudinal course of PTSD, while simultaneously examining whether pre-disaster Axis I psychiatric disorders and history of manageable stressors influence vulnerability to develop post-disaster PTSD or subclinical symptomatology.